This invention relates to optical devices, and more particularly to optical transmitters and/or optical receivers.
Optical transponders include a combination of at least one optical transmitter and at least one optical receiver thereby providing input/output functions in one device. The use of optical networks is increasing. The bandwidth of the signals that optical transmitters can transmit, and the bandwidth of the signals that optical receivers can receive, is progressively increasing.
It is often important that optical devices such as optical transmitters and optical receivers be miniaturized. Miniaturization of optical devices is challenging. For example, positioning components close together may cause electromagnetic interference (EMI) of one optical device (or component thereof) to interfere with another optical device (or component thereof). Additionally, the amount of heat that is generated (and thus has to be dissipated) is similar regardless of the size of the component. As such, miniaturized optical devices have to dissipate more heat for a given volume. As such, many designs employ thermoelectric coolers to control thermal exposure of critical optical elements such as lasers. Alternatively, they may have distinct heat generating devices (such as lasers and laser drivers within optical transmitters) separated by a considerable distance or in separate packages. However the laser driver supplies a radio-frequency electrical signal to the laser, and as such is located relatively close thereto. Spacing the components within an optical device may also result in electrical conductors that extend between certain ones of the components. An extended electrical conductor can act as a transmitting or receiving antenna of EMI or a parasitic element degrading high frequency performance.
Optical transmitters and optical receivers typically include both optical and electronic (microwave) portions. In optical transmitters, an electrical signal received and processed by the electronic portion is converted into an optical signal and then transmitted over an optical fiber cable. In optical receivers, an optical signal received over an optical fiber cable is processed by the microwave portion and then transmitted as an electrical signal.
A design challenge involves repairing, replacing, or updating any optical device that is mounted to a circuit board. It would be desired to effectively replace one optical device (having both electronic and mechanical connections) by another optical device. Removal of an optical device involves not only mechanical connections, but electrical connections between the optical device and the circuit board must also be disconnected. To insert a replacement optical device, the applicable optical device similarly is secured by providing a mechanical connection as well as an electrical connection to the circuit board.
Materials play an important role in the design of optical devices. The device packages that enclose optical transmitters or optical receivers must adapt to a variety of mechanical, thermal, electrical, and optical conditions. For instance, the different portions of the device package are configured to withstand thermomechanical stresses, vibrations, and strains that are applied by, e.g., outside forces to the device package which houses the optical device. It is also required that different parts of the optical device can tolerate different thermal expansions that would otherwise create excessive stresses or strains in the device package resulting in optical instability. Thermal conditions also relate to the capability of operating successfully at a series of high or low temperatures, depending on the application. Additionally, the optical device has to provide the optical and electrical functions for which it is designed. As such, the materials selected play an important role in allowing the optical device to perform its desired function.
In one aspect, it would be desired to provide an optical device that is designed to operate under the variety of thermal, mechanical, optical, and/or electrical conditions that the optical device will potentially encounter over its life. In another aspect, it would be desired to provide a Faraday cage to limit the transmission of electromagnetic interference through a part of a device package case of an optical transmitter or optical receiver. In yet another aspect, it would be desired to provide effective heat sinking from one or more heat generating components within an optical component. In yet another aspect, it would be desired to provide an effective surface mount to secure an optical transmitter or optical receiver to a circuit board.
One aspect includes an optical transmitter, an optical receiver, a circuit board, a first thermally conductive and electrically insulative adhesive pad, and a second electrically and thermally conductive adhesive pad. The circuit board includes a first mounting region and a second mounting region. The first mounting region is configured for mounting the optical transmitter and the second mounting region is configured for mounting the optical receiver. The first adhesive pad includes two substantially planar faces. Each one of the planar faces of the first adhesive pad is coated with an adhesive that facilitates a first affixing of the optical transmitter to the first mounting region whereby the optical transmitter remains affixed through a range of operating temperature and pressures. The first adhesive pad has a first prescribed thickness. The optical transmitter is configured to allow electrical and optical mounting when the first adhesive pad secures the optical transmitter to the circuit board. The second adhesive pad includes two substantially planar faces. Each one of the planar faces of the second adhesive pad is coated with an adhesive that facilitates a second affixing of the optical receiver to the second mounting region whereby the optical receiver remains affixed through a range of operating temperature and pressures. The second adhesive pad has a second prescribed thickness. The optical receiver is configured to allow electrical and optical mounting when the second adhesive pad secures the optical receiver to the circuit board.
In accordance with another aspect, a Faraday cage is configured to enclose the optical device. The Faraday cage extends between a baseplate and a lid. The lid is vertically spaced from the baseplate. The Faraday cage limits the passage of EMI. The Faraday cage includes one or more ceramic wall portions and a plurality of vias. The ceramic wall portions extend from the baseplate to the lid and limit the passage of EMI through the ceramic wall portions. The ceramic wall portions include a plurality of laminated ceramic layers. The plurality of vias extend substantially perpendicular to the baseplate through the laminated ceramic layers. Each one of the plurality of vias extends substantially from the baseplate to the lid. The vias are configured to form a pattern that limits the passage of EMI through the vias. In one embodiment, the baseplate, lid, and one or more ceramic wall portions define a Faraday cage that surrounds an optical device.